Electrochemical devices for the separation of air are employed in several modes of operation. Commonly such devices employ an yttrium stabilized zirconia electrolyte or a cerium gadolinium oxide zirconia electrolyte sandwiched between two porous electrodes. When an electric current is applied to the electrodes and air is introduced to the electrode serving as a cathode, oxygen within the air ionizes and is transported through the membrane to the opposite side of the electrode in contact with the anode electrode. The oxygen ions recombine into elemental oxygen and in so doing give up their excess electrons to the anode electrode. In other electrochemical air separation devices, a conductor connects the electrodes and the driving force is a partial pressure differential between the cathode and the anode electrodes. In yet a further electrochemical air separation device employed as a fuel cell, fuel is introduced to the anode electrode that reacts with the oxygen to establish a partial pressure differential. Combustion of the fuel is supported by the separated oxygen. The electrons passing through the conductor can be channeled towards a load for generation of electric power.
It has been found that electrochemical devices will degrade over a period of time. One major reason for this is hydrogen sulfide and sulfur oxides contained in the air. The sulfur oxides will combine with the yttrium stabilized zirconia to produce small electrolyte defects that will allow the air to pass from the cathode to the anode side. Since no oxygen ionization occurs, performance is degraded.
It is well known in the art to filter particulates to maintain proper operation of the electrochemical air separation device. For instance, the use of a filter with respect to electrochemical devices for filtration of particulate matter is referenced in U.S. Pat. Nos. 6,352,624, 5,332,483 and 5,205,990. In U.S. Pat. No. 6,432,177 a filter system is disclosed in connection with a fuel cell that has a particulate filter that can be a layered structure including a high efficiency particulate accumulation filter and several sheets of coarser filter medium to filter out particulate matter. Located downstream of this filter is a chemical filtering portion that is designed to trap acidic compounds such as sulfur oxide. It is envisioned in this patent that adsorbent materials are used that include a carrier that can be a metal oxide.
The central problem with filtering system of the prior art is that eventually they become heavily laden with chemical and physical contaminants and need to be replaced. It is therefore desirable that the filter system be constructed simply and as inexpensively as possible. Working against this is that for chemical adsorption to take place, the filter must have a high surface area to contain a sufficient amount of an active component such as an adsorbent. However, to have a high surface area for a filter element, the porosity must be increased by increasing the number of pores and therefore decreasing the pore sizes. However, as pore sizes decrease, it becomes difficult to form deposits of such active component without closing off the pores. Moreover, in use of the filter, the small pores can become clogged with reaction components as well as particulate matter of the active component that has broken off of the substrate.
As will be discussed, the present invention provides an inexpensive filter system for an electrochemical air separation device that can easily and inexpensively be replaced in that employs a chemical filtering section of high surface area that is specifically designed to filter or trap airborne contaminants such as sulfur dioxide and hydrogen sulfide.